Image reading apparatuses such as an image scanner and copying machine use an image sensor that optically reads image information of an original and converts the information into an electrical signal. A general image sensor is a contact image sensor unit (to be referred to as a CIS unit hereinafter) that has a linear shape and reads an original at a close distance without changing the size (patent reference 1).
FIG. 10 depicts a view for explaining the structure of the conventional CIS unit by its section.
A CIS unit 100 reads an image of an original 102 placed below a transparent glass plate 103. The unit 100 has, inside a molded product 104, a linear light source 105 that illuminates the surface of the original 102, and a lens array 107 that forms an image of the reflected light from the original surface on a linear photoelectric conversion element 108. The unit 100 further includes, for example, a rectangular substrate 110 on which the linear photoelectric conversion element 108 and a driver and controller of the photoelectric conversion element 108 are mounted. The molded product 104 is made of a thermoplastic resin from the viewpoints of molding properties and economy (patent reference 2).
In this CIS unit, a read line 109 on the original 102 illuminated with the linear light source 105, the lens array 107, and the photoelectric conversion element 108 are accurately positioned on the same optical axis. Also, the optical distances between these components are determined, and their positions and distances must be accurately maintained. As demands for high-resolution in image reading apparatuses increase in recent years, the components of the CIS unit are incorporated into the molded product 104 with higher dimensional accuracy, and a demand has arisen for a CIS unit having higher dimensional accuracy.
The substrate 110 has, for example, a power supply unit (not shown) of the linear light source 105 and a signal input/output unit (not shown), in addition to the photoelectric conversion element 108, and also has various electronic components. In addition, conductor wirings that connect these parts are formed by patterning, and circuits that drive the photoelectric conversion element 108 and linear light source 105 in accordance with external power supply and signal supply are also formed.
FIGS. 9A and 9B depict views for explaining a method of fixing this substrate to the molded product.
As shown in FIG. 9A, the substrate 110 is fixed by thermal caulking to the molded product 104 made of a thermoplastic resin. In this case, the substrate 110 is thermally caulked to the molded product 104 by a plurality of caulking projections 112 projecting from the upper surface of the molded product 104, thereby forming a thermally caulked combined structure 101 (FIG. 9B) as the CIS unit 100 (FIG. 10). The thermally caulked combined structure 101 functions as the CIS unit 100 shown in FIG. 10 described above. Patent reference 3 describes details of the thermal caulking method that fixes a part as an object to be fixed by caulking by using the caulking projections 112 formed on the surface of the molded product 101 made of a thermoplastic resin.    Patent reference 1: Japanese Patent Laid-Open No. 2006-287923    Patent reference 2: Japanese Patent Laid-Open No. 07-162587    Patent reference 3: Japanese Patent Laid-Open No. 2001-018295